Coordinated regulation of floral transition by protein and long noncoding RNA components Project Summary Epigenetic mechanisms enable the genome to adapt to developmental and environmental cues. Flowering is one of the major developmental commitments in the plant life cycle. Plants have evolved intricate regulatory networks to control flowering time in response to both endogenous and environmental conditions. We use the floral transition as a model system to study epigenetic regulation of gene expression in eukaryotes. Recent recognition of long noncoding RNAs (lncRNAs) in eukaryotes and growing examples of their function in various developmental programs indicate that lncRNAs play roles in developmental programs, carcinogenesis and other human diseases. Despite some well-characterized examples, mechanistic details of lncRNAs and their underlying roles in development are not well understood. Our recent study identified the first functional lncRNA in plants, which is necessary for the proper epigenetic silencing of a developmentally regulated gene, FLC. Here we seek to understand mechanistic details on the role of lncRNAs in development. Our proposal is to elucidate structural and regulatory components governing protein-lncRNA mediated epigenetic regulation of developmental genes. Our overriding goals are built around three specific aims: 1) Identify and characterize lncRNAs, 2) Study mechanisms in which protein and RNA components are coordinated to regulate developmental genes, 3) Employ genetic approaches to address the mechanisms to sense and measure the duration of environmental changes (i.e. cold), which are upstream events of protein-lncRNAs mediated regulation of developmental gene expression. Our approach to dissect the mechanistic details of lncRNA- mediated epigenetic regulation will be useful not only for understanding a key mechanism of plant development (i.e. flowering) but also for elucidating the mechanism of epigenetic regulation of gene expression which has a deep evolutionary root among eukaryotes.